The invention relates to grates in general, particularly to improvements in grates for industrial furnaces. The invention also relates to improvements in grate bars which can be used in such grates to support and to admit oxygen into a layer of coal or other solid fuel.
It is known to provide a grate bar with a passage which admits atmospheric air into the fuel layer on the grate bar. It is also known to provide the grate bar with an upward extension having an opening for admission of air into the fuel layer. Rows of such grate bars are assembled into a grate which must prevent particles of fuel and/or combustion products from descending into the space below the grate because this could entail rapid contamination of the furnace by fuel, ashes, cinder and like substances and would interfere with movements of grate bars relative to each other. On the other hand, the grate should ensure a substantially uniform distribution of oxygen in the fuel layer on the top walls of the grate bars. Heretofore known grates and grate bars cannot fully satisfy the above seemingly conflicting requirements, i.e., they either favor uniform distribution of oxygen while permitting a relatively large quantity of fuel and/or combustion products to descend through the grate or vice versa.
Attempts to overcome the aforediscussed drawbacks of conventional grates include such orientation of openings in the extensions of the top walls of the grate bars that the streams of oxygen flow rearwardly in the longitudinal direction of the grate bars. This creates problems in connection with certain types of fuel, e.g., when the fuel contains paper, plastics and like relatively lightweight constituents which are blown into the rear portion of the furnace and cannot be fully combusted on the grate. Another drawback of such proposal is that the particles of fuel and/or combustion products are likely to clog the openings in response to forward and rearward movements of the grate bars in a manner which is customary in many types of grates for use in industrial furnaces. This will be readily appreciated because the open end of each opening advances directly into the adjacent mass of fuel and/or combustion products during rearward movement of the respective grate bar and/or during forward movement of the immediately following grate bar. The mechanism which reciprocates the grate bars will cause particles of fuel and/or combustion products to penetrate into and to jam in the openings so that the rate of oxygen flow into the fuel layer is unduly affected with attendant reduction of the percentage of fully combusted fuel.